This invention relates to a method for the control of aero gas turbine engines in aircraft having at least two such engines.
In certain flight phases, some engine frequencies can excite vibrations in the aircraft, these being caused by the rotational speed of the high-pressure shaft (NH) or the low-pressure shaft (NL), respectively. These vibrations are perceived by the passengers as noise or oscillations. Also, since the engines rarely operate at the same rotational speed, interference can occur between the engines. This gives rise to beats or standing waves. Where the rotational speed of the low-pressure shaft is controlled, i.e. only the low pressure compressors are synchronized, the rotational speed of the high-pressure shaft will remain a potential cause of disturbance.
Among others, the causes for different engine behavior are: The disparity of age between engines upon replacement of one of the engines. Inaccuracies in the measured quantities, these resulting in the generation of deviant controlled variables. The unavoidable manufacturing tolerances which entail similar effects.
Normally, aero engines are both considered and controlled individually. Only in specific cases, the interaction of aero engines is taken into consideration, for example in emergency or thrust vectoring situations.
Few cases are known in which both engines are linked together in terms of control during operation. For example, in the case of a failure of the vertical rudder, the two engines can be operated with different thrust, this enabling turns to be flown. Also, thrust vectoring is known in military applications (cf. U.S. Pat. No. 5,769,317 or U.S. Pat. No. 6,105,901, for example).
The state of the art entails many, significant disadvantages. It does not provide for the interaction between two or more engines while making use of the components already available in the engines and in the aircraft. This deficiency leads to a higher noise level in the aircraft cabin. Aircraft manufacturers have to fit more attenuation material, resulting in higher mass and increased costs. Furthermore, higher investments have to be made into vibration reduction during aircraft development.